The present invention relates to a multi-piece solid golf ball composed of a core, an envelope layer, an intermediate layer and a cover that have been formed as successive layers. More specifically, the invention relates to a multi-piece solid golf ball which has a satisfactory flight performance and controllability when used by professionals and other skilled golfers, is able in particular to maintain a straight trajectory on full shots, and has an excellent scuff resistance.
A variety of golf balls have hitherto been developed for professionals and other skilled golfers. Of these, multi-piece solid golf balls in which the hardness relationships among layers encasing the core, such as an intermediate layer and a cover layer, have been optimized are in wide use because they achieve both a superior distance in the high head speed range and good controllability on shots taken with an iron and on approach shots. Another important concern is the proper selection of thicknesses and hardnesses for the respective layers of the golf ball in order to optimize flight performance, the feel of the ball when played, and the spin rate of the ball after being struck with a club, particularly given the large influence of the spin rate on control of the ball. A further key concern in ball development, arising from the desire that golf balls also have durability under repeated impact and suppress burr formation on the ball surface (have improved scuff resistance) when repeatedly played with different types of clubs, is how best to protect the ball from external factors.
The three-piece solid golf balls having an outer cover layer formed primarily of a thermoplastic polyurethane that are disclosed in, for example, JP-A 2003-190330, JP-A 2004-049913, JP-A 2004-97802 and JP-A 2005-319287 were intended to meet such needs. However, these golf balls fail to achieve a sufficiently low spin rate when hit with a driver; professionals and other skilled golfers desire a ball which delivers an even longer distance.
Meanwhile, efforts to improve the flight and other performance characteristics of golf balls have led to the development of balls having a four-layer construction, i.e., a core enclosed by three intermediate and cover layers, that allows the ball construction to be varied among the several layers at the interior. Such golf balls have been disclosed in, for example, JP-A 9-248351, JP-A 10-127818, JP-A 10-127819, JP-A 10-295852, JP-A 10-328325, JP-A 10-328326, JP-A 10-328327, JP-A 10-328328, JP-A 11-4916 and JP-A 2004-180822.
Yet, as golf balls for the skilled golfer, such balls have a poor balance of distance and controllability or fall short in terms of achieving a lower spin rate on shots with a driver, thus limiting the degree to which the total distance can be increased.
Moreover, in the multi-piece solid golf ball described in U.S. Pat. No. 6,994,638, the thickness and hardness relationships among the respective layers such as the intermediate layer and the cover are not disclosed. This ball is thus inadequate for achieving the spin rate-lowering effect on shots with a driver that is desired in a golf ball for the skilled golfer.
Each of the golf balls disclosed in JP-A 2001-17569, U.S. Pat. No. 6,416,425 and JP-A 2001-37914 is a multi-piece solid golf ball of five or more layers in which the four or more layers encasing the core, such as envelope layers and cover layers, have various hardness relationships. Yet, owing to the fact that the envelope layers are made of resin materials and to the differing hardness relationships and thickness relationships among the respective layers, such balls fail to achieve the performance needed in a golf ball for skilled players.